net mask calculator

IPv4 Net Mask Calculator

Enter an IPv4 address and a subnet value as CIDR (/24) or dotted mask (255.255.255.0). You can also type CIDR directly with the IP, like 192.168.1.50/24.

IP Address

Subnet (CIDR or Dotted Mask)

A net mask calculator helps you convert an IPv4 address and subnet into practical network details. Instead of manually doing binary math, you can instantly find the network address, broadcast address, host range, wildcard mask, and the number of usable hosts.

Why a Net Mask Calculator Matters

If you build or maintain networks, subnetting shows up everywhere: office LANs, cloud VPCs, VPNs, firewall rules, and routing tables. A small mask mistake can break connectivity or create overlapping networks. This calculator helps you avoid those errors and quickly validate your configuration.

Plan subnets for departments, VLANs, or projects
Verify router and firewall ACL ranges
Understand broadcast domains
Troubleshoot host reachability issues
Check private vs public addressing decisions

How to Use This Tool

Enter a valid IPv4 address (for example, 10.20.30.40).
Enter either CIDR prefix (like /16) or dotted decimal mask (like 255.255.0.0).
Click Calculate.
Review network details including first and last usable host addresses.

Subnetting Fundamentals (Quick Review)

IP Address + Netmask = Network Boundary

An IPv4 address is 32 bits. The subnet mask tells you which bits represent the network and which represent hosts.

Network bits: fixed portion shared by all hosts in the subnet
Host bits: variable portion assigned to devices

CIDR Notation

CIDR uses a slash and prefix length. Example: /24 means 24 bits are network bits. Equivalent dotted mask is 255.255.255.0.

Common CIDR to Netmask Values

/8 → 255.0.0.0
/16 → 255.255.0.0
/24 → 255.255.255.0
/25 → 255.255.255.128
/26 → 255.255.255.192
/27 → 255.255.255.224
/28 → 255.255.255.240
/29 → 255.255.255.248
/30 → 255.255.255.252
/31 → 255.255.255.254
/32 → 255.255.255.255

Example Calculation

Example: 192.168.10.77/26

A /26 mask means each subnet has 64 total addresses. The address 192.168.10.77 falls inside the subnet:

Network: 192.168.10.64
Broadcast: 192.168.10.127
Usable host range: 192.168.10.65 to 192.168.10.126
Usable hosts: 62

Common Subnetting Mistakes

Using non-contiguous masks (invalid masks)
Forgetting that network and broadcast are reserved in most IPv4 subnets
Mixing up wildcard mask and subnet mask in ACL configs
Overlapping subnet assignments across sites
Assuming /31 or /32 behave like standard multi-host LAN subnets

FAQ

Is this an IPv6 calculator?

This page is focused on IPv4 netmask calculations. IPv6 uses prefix lengths too, but address representation and subnet logic are different.

What is a wildcard mask?

Wildcard mask is the inverse of the subnet mask. It is commonly used in access control lists (ACLs), especially on network devices.

Can I enter either CIDR or dotted mask?

Yes. The calculator accepts both formats and normalizes them into complete subnet information.

Final Thoughts

A reliable subnet mask calculator saves time and reduces risk when working with IP planning, routing, and network troubleshooting. Keep this tool handy whenever you need fast, accurate IPv4 subnet details.